Im checking out the KSP Interstellar Mod at the moment, so I was wondering if Im able to build a SSTO with it: Result: You need at least the upgraded fission Reactors and the upgraded Thermal Turbojet (works like the Rapier). It has some odd flight-pattern for Orbit and its range is pretty bad compared with stock-only-SSTOs, BUT: Dock it on a Craft and sent it to Duna or Laythe and enjoy flying there for a very long time The Engine will also run in Eves Atmosphere, but I havent checked if I can make it back to Orbit. Another Feature is, that this plane isnt stalling at all.